The World Health Organization is investigating a report that Chinese farmers are giving a drug meant for humans to their chickens, in an effort to prevent the spread of bird flu. The Chinese government says it's also investigating

If large numbers of chickens are given medicine meant for humans to protect them against a lethal strain of bird flu, then the virus can become stronger and more resistant. That means the drug may no longer offer protection to humans.

Dr. Hendrick Bekedam of the World Health Organization fears that's already happening. "We are more and more concerned that this anti-viral might not be that useful anymore at the moment that we'll be needing it for treatment of humans."

The WHO is looking into an American newspaper report that alleges Chinese farmers gave the drug Amantadine to their chickens for years, with the encouragement of the Chinese government.

Beijing denies the report. But there is evidence Amantadine has been misused.

Dr. Leon Lai is an infectious diseases specialist at Washington Hospital Center in Washington, DC, "If these are drugs that are supposedly only given to humans, why would these chickens be producing viruses that are resistant? And I think this is the answer to that mystery."

The H-5-N-1 strain of bird flu emerged in Southeast Asia eight years ago, and millions of chickens have been slaughtered to prevent the virus from spreading. In rare cases birds have transmitted the virus to humans, resulting in 54 deaths. But the greatest fear is that the bird flu will mutate to a form that could spread from human to human, leading to a worldwide pandemic.

Amantadine would have been by far the cheapest, most readily available, drug for treatment.

Dr. Lai says,"If you knock out one of these, you basically knock out a huge portion of the amount of tools we have to quarantine and contain an outbreak."

The World Health Organization has consistently recommended that Amantadine be reserved for human use only.

Dr. Lai says that if the Chinese government did advocate using the drug in chickens, it must have known it was violating international guidelines. "To flout that and to assume that you knew better than the worldwide scientific body of opinion would, I think, be very irresponsible."

The World Health Organization estimates a bird flu outbreak among humans could kill up to 50 million people worldwide.